(a) Technical Field
The present disclosure generally relates to a canister purge control method for a vehicle, more particularly, to the canister purge control method by which the number of components of an active purge system provided in the vehicle can be reduced.
(b) Description of the Related Art
As is well known in the art, in a fuel tank of a vehicle, gas is produced by evaporation of fuel, i.e., fuel evaporation gas containing fuel components, such as hydrocarbon (HC). Thus, the vehicle is provided with a canister for collecting and storing the fuel evaporation gas so as to reduce air pollution that may result from the fuel evaporation gas in the fuel tank.
The canister is constructed by filling a container with an absorbent material able to absorb the fuel evaporation gas that has been introduced from the fuel tank. Activated carbon is widely used as the absorbent material Activated carbon acts to absorb hydrocarbon or the like, i.e., a fuel component, of the fuel evaporation gas introduced into the container of the canister.
The canister is configured such that the fuel evaporation gas is absorbed by the absorbent material when the engine is stopped, and the fuel evaporation gas is detached from the absorbent material using air pressure taken from the outside (i.e., atmosphere) when the engine is running, so that the detached fuel evaporation gas can be supplied together with the air to an intake system of the engine.
The operation of taking in the fuel evaporation gas, collecting it in the canister, and supplying the fuel evaporation gas and the air to the engine is referred to as a purge operation, and the gas taken into the engine from the canister is referral to as purge gas. The purge gas may be a mixture in which fuel components, such as hydrocarbon, detached from the absorbent material of the canister, are mixed with air.
In addition, in a purge line connecting a purge port of the canister and the intake system of the engine, a purge control solenoid valve (hereinafter referral to as “PCSV”) that controls the purge operation is provided.
The PCSV opens in response to the purge operation while the engine is running. According to this configuration, the fuel evaporation gas created in the fuel tank is collected in the canister, purged to the intake system of the engine via the open PCSV, and consumed or burned in the engine.
The PCSV is controlled by a control unit, e.g. an engine control unit (ECU). The PCSV is controlled so that the PCSV is opened and closed (i.e., the purge operation is turned on and off) or the degree of opening of the PCSV is adjusted, depending on the driving status of a vehicle to control a flow of the fuel evaporation gas.
A typical configuration of the canister will be described herein. The canister includes a container filled with an absorbent material (e.g., activated carbon). In addition, a purge port, a loading port, and an air port are provided on the container. The purge port is connected to an intake system of an engine, such that fuel evaporation gas is supplied toward the engine therethrough. The loading port is connected to a fuel tank, such that fuel evaporation gas is introduced from the fuel tank therethrough. The air port is connected to an air filter (i.e., a canister filter), such that air is taken into the container from the atmosphere therethrough.
A diaphragm is disposed in the inner space of the container to divide the inner space into a space in which the air port is located and a space in which the purge port and loading port are located. The fuel evaporation gas, which is introduced through the loading port from the fuel tank, is directed to pass through the inner space divided by the diaphragm. As a result, hydrocarbon, which is a fuel component, is absorbed by the absorbent material.
In addition, when intake pressure, i.e., engine negative pressure, is applied from the intake system of the engine to the inner space of the canister through the purge port in response to the PCSV being opened by the control unit during the running of the engine, air is taken in through the air filter and the air port, and fuel evaporation gas, detached from the absorbent material, is discharged through the purge port to be taken into the engine.
In the purge operation of taking air from the atmosphere into the canister and detaching and carrying fuel components, such as hydrocarbon, from the absorbent material in the canister into the engine due to intake air, engine negative pressure is required to be applied to the canister through the purge line and the purge port.
However, the current tendency is toward reducing the number of purge operations of an engine in order to improve the fuel efficiency of vehicles. In particular, in continuously variable valve lift (CVVL) engines or hybrid electric vehicle (HEV)/plug-in hybrid electric vehicle (PHEV) engines, a reduced engine negative pressure area necessarily reduces the number of purge operations.
In addition, in vehicles provided with a turbocharger, an engine intake system, such as an intake manifold, has a relatively low negative pressure. In this case, the purge operation of the canister may be difficult.
Accordingly, an active purge system is known as a solution of the above-described problem. The active purge system is advantageous for vehicles in which the negative pressure of the intake system of the engine alone is insufficient for the purge performance and efficiency of the canister, e.g., HEV/PHEV vehicles and turbocharger vehicles, which are environmentally friendly vehicles, and turbocharger vehicles, as well as the other types of combustion engine vehicles.
In the active purge system, an active purge pump (APP) is disposed on a conduit (i.e., a purge line) connecting the purge port of the canister and the engine intake system to take in and transfer purge gas from the canister to the engine.
In the active purge system, sensors are disposed on conduits on the front and rear end sides of the pump. A control unit actively controls the operation of the pump, based on values measured by the sensors. Consequently, the purge operation of the canister can be properly performed even in conditions in which the negative pressure of the engine intake system is insufficient.
However, when the active purge system is applied, not only the pump, but also a plurality of sensors, such as pressure sensors, must be additionally provided on conduits on the front and rear end sides of the pump to control fuel evaporation gas, thereby disadvantageously increasing the cost of the vehicle.